WASHINGTON (CNN) -- Defense Secretary Donald Rumsfeld on Wednesday dismissed as "reprehensible" Amnesty International's characterization of the U.S. detention facility at Guantanamo Bay, Cuba, as "the gulag of our times."

The human rights monitoring group made the accusation in a report released May 25.(Full story)

"The detention facility at Guantanamo Bay has become the gulag of our times, entrenching the practice of arbitrary and indefinite detention in violation of international law," said Irene Khan, Amnesty's secretary-general.

At a Pentagon news conference, Rumsfeld defined a gulag as where the Soviets "kept millions in forced labor concentration camps" and what some considered life to be under Saddam Hussein's regime in Iraq.

"To compare the United States and Guantanamo Bay to such atrocities cannot be excused," he said. "Free societies depend on oversight, and they welcome informed criticism, particularly on human rights issues. But those who make such outlandish charges lose any claim to objectivity or seriousness.

"The Washington Post, to its credit, rejected the comparison between Guantanamo and a gulag in a recent editorial."

More than 540 detainees from 20 countries are in U.S. custody at Guantanamo Bay.

While acknowledging some instances of detainee abuse, Rumsfeld criticized media efforts for failing to place the issue in a "proper context."

"Precious little has been written by [newspaper] editorial boards about the beheading of innocent civilians by terrorists, the thousands of bodies found in mass graves in Iraq, the allegations of rape of women and girls by U.N. workers in the Congo," he said.

The defense chief said a minuscule percentage of U.S. service members in Iraq, Afghanistan and Guantanamo Bay "have been found to have committed illegal acts against detainees."

"To date there have been approximately 370 criminal investigations into the charges of misconduct involving detainees out of 68,000 detainees that have been in U.S. custody over the period since September 11."

He said that Guantanamo detainees are suspected terrorists with many "systematically trained to lie and to claim torture."

"At least a dozen of the 200 already released from Gitmo have already been caught back on the battlefield involved in efforts to kidnap and kill Americans," he said.

Rumsfeld defended U.S. efforts to establish guidelines and proper procedures on how to accommodate detainees' religious practices -- a development he said has not received nearly the publicity of a retracted Newsweek report alleging the flushing of a Quran down a toilet.

"Copies of these instructions have been publicly available, but they have received comparatively little media attention. I have not yet seen a complete printing of those instructions in any journal. This lack of media attention to U.S. policy guidance to treat detainees humanely creates misperceptions," he said.

"But to try to equate the military's record on detainee treatment to some of the worst atrocities of the past century is a disservice to those who have sacrificed so much to bring freedom to others."

On Tuesday, President Bush called the Amnesty International report "absurd." (Full story)

Vice President Dick Cheney also said Amnesty's condemnation of the United States offended him.

"For Amnesty International to suggest that somehow the United States is a violator of human rights, I frankly just don't take them seriously," Cheney said in an interview that aired Monday on CNN's "Larry King Live." (Full story)

In response to Bush's remarks, Amnesty International on Tuesday said evidence continues to mount that the United States is "running a network of detention centers where people are held in secret or outside any proper legal framework."

The group said that the United States "has operated an isolated prison camp [at Guantanamo] in which people are confined arbitrarily, held virtually incommunicado, without charge, trial or access to due process. Not a single Guantanamo detainee has had the legality of their detention reviewed by a court, despite the Supreme Court ruling of last year."

The U.S. high court ruled last year that detainees at Guantanamo Bay have a right to challenge their imprisonment but left it to lower courts to handle individual appeals.